President Barack Obama escalated U.S. economic sanctions against Russia on Tuesday for its aggression against Ukraine but dismissed suggestions the growing chill in U.S.-Russian relations marked the start of a new Cold War.

The United States and the European Union, in a carefully coordinated action, announced targeted new sanctions against Russian banks, energy and defense firms.

It was the West's most serious response yet to what it calls Russian instigation of and continuing support for the separatist uprising in the east and the shootdown of a Malaysian passenger jet on July 17 over eastern Ukraine.

Obama, speaking at the White House, said the sanctions will have a "greater impact on the Russian economy than we've seen so far" in a drive to force Moscow to stop backing the separatists.

Until now Europe had stopped short of tougher steps against Russia for fear of retaliation. Obama said the new sanctions were a sign of "the waning patience Europe has with nice words from President (Vladimir) Putin that are not matched by actions."

Senior U.S. officials voiced growing alarm about a Russian troop buildup on the border with eastern Ukraine and a continued supply of heavy weaponry to the separatists.

These are signs that, so far at least, the sanctions are not forcing Putin to back down despite the damage the sanctions are doing to the Russian economy.

"It's not a new Cold War," Obama told reporters. "What it is, is a very specific issue related to Russia's unwillingness to recognize that Ukraine can chart its own path."

The new targets for sanctions included VTB, the Bank of Moscow, the Russian Agriculture Bank and the United Shipbuilding Corp., the Treasury Department said.

The sanctions on the three banks prohibit U.S. citizens or companies from dealing with debt carrying maturities longer than 90 days, or with new equity.

Five of the six largest state-owned banks in Russia are now under U.S. sanctions.

Also targeted was United Shipbuilding Corp, a shipbuilding company based on St. Petersburg, in a move that freezes any assets it may hold in the United States and prohibits all U.S. transactions with it.

The Commerce Department classified United Shipbuilding Corp as a defense technology company.

The new sanctions block the exports of specific goods and technologies to the Russian energy sector. The Commerce Department said it will deny any export, re-export or foreign transfer of items for use in Russia's energy sector that may be used for exploration or production